1. Field of the Invention
The present invention relates to an image pickup apparatus such as a video camera.
2. Related Background Art
In recent years, video cameras have become remarkably popular since they have compact, lightweight structures, variable magnifications, and multifunctions.
In the above-mentioned video camera, most functions associated with an image pickup operation are automated. Therefore, an unsuccessful image pickup operation caused by the functions of the video camera itself rarely occurs.
The video camera is most frequently used in a hand held state. In this state, the frame may be considered to be always vibrated. In recent years, degradation of image quality caused by the frame vibration, and an uncomfortable situation such as “video sickness” are discussed as problems.
As a means for eliminating the above-mentioned frame vibration, an image stabilization device utilizing a gyro mechanism is conventionally known.
In this device, a lens barrel system is movably supported by a gyro mechanism to obtain a stable image. However, this device makes the camera main body bulky, and also causes an increase in weight.
In recent years, an image pickup apparatus, which comprises image vibration correction means comprising optical axis decentering means, such as a variable angle prism, for decentering an optical axis of an image pickup optical system according to a vibration of a camera and thereby locating an optical image on a predetermined focal plane of an image pickup element, has been developed.
The variable angle prism has the following structure. That is, a liquid having a given refractive index is sealed in an accordion-like chamber having a bellows clamped between two transparent plates. The transparent plate on the object side is tilted by a driving mechanism comprising a magnetic circuit, thereby decentering a photographing optical axis.
In the above-mentioned apparatus, since the optical axis is decentered by the variable angle prism, a lens barrel system need not be moved, and increases in the size and weight of the camera main body can be minimized. Thus, a good image can be obtained by effectively preventing an image vibration.
In the above-mentioned apparatus, since an image vibration correction is performed by tilting the transparent plate of the variable angle prism by the driving mechanism comprising the magnetic circuit, power consumption is increased as compared to a normal photographing mode. Thus, a demand has arisen for efficient battery saving means.
In addition, the apparatus using the variable angle prism suffers from the following problem.
In the image pickup apparatus comprising the image vibration correction means, e.g., the optical axis decentering means such as the variable angle prism, when the image vibration correction mode is disabled during an image recording operation, a tilting state by the driving mechanism for driving the transparent plate is released, and a centering operation occurs. That is, the two transparent plates become parallel to each other due to liquidity of the liquid sealed between them.
For this reason, discontinuous finder images are formed, and a user may feel uneasy.